1. Field of the Invention
The embodiments discussed herein are directed to a semiconductor device that is suitable for use in a lateral double-diffused metal-oxide-semiconductor field-effect transistor (LDMOSFET) such as power MOSFET.
2. Description of Related Art
The voltage of a power supply used for a CPU of a computer or the like tends to become lower. Accordingly, a power supply circuit with a synchronous rectification system has been widely used. Power supply circuits use either a diode rectification system or a synchronous rectification system. In the diode rectification system, the conversion efficiency (loss) of a power supply circuit is determined based on the forward voltage and the output current of a diode. When a large current is output, a loss at an output rectification portion increases and thus a heat sink for the heat generated by the loss is necessary. In the synchronous rectification system, for example, a power MOSFET having a high switching speed is used for main switching, and a switch function is synchronized.
An exemplary power MOSFET includes an LDMOSFET having an insulating film, which is larger than that of a gate insulating film and is provided between a gate electrode and a drain layer, the parasitic capacitance of which is decreased. In the LDMOSFET, a breakdown voltage between a source and a drain is ensured, and an on-resistance is decreased. Therefore, LDMOSFETs are suitable for switching at a high speed or a high frequency.
When the switching speed of an LDMOSFET is important, a gate insulating film having a small thickness is provided. When the gate breakdown-voltage is important, a gate insulating film having a large thickness is provided. When an integrated circuit including a plurality of LDMOSFETs, which includes gate insulating films having different thicknesses, are manufactured in the fewest possible processes, forming a body region without depending on the thicknesses of the gate insulating films is necessary.
For example, Japanese Laid-open Patent Publication Nos. 2006-13344 and H11-163320 disclose related arts.